The present invention pertains to a process for preparing a foamed polymer, by reacting glycerol with a tri-carboxylic acid.
Polymer foams are known in the art for various applications, e.g., as packaging material and as insulation material.
A disadvantage of polymer foams known in the art is that they are often based on petroleum-derived sources, which means that they are not renewable, and cannot be classified as “green”. A further disadvantage is that they are not biodegradable, which is of particular importance for packaging materials. A still further disadvantage is that some of the materials comprise heteroatoms or aromatic rings, which may cause issues when the material is combusted, such as the formation of SOx/NOx compounds and the release of toxic fumes or other toxic compounds into the environment.
There is therefore need for a polymer foam which solves these problems.
WO2010/059925 describes a polymer obtained by reaction of glycerol with citric acid in a two-step process. In a first step, low-molecular weight polyester pre-polymers are synthesized at a temperature of 80° C. to 250° C., which are then reacted further at a pressure at or above 1 atmosphere and a temperature of 175° C. to 400° C.
It has been found, however, that the polymer and process as described in this reference have a number of disadvantages. In particular the resulting foamed product has an irregular structure. Further, it turns out that the polymer is difficult to produce in a controlled and reproducible manner.
There is therefore need for a process for producing a glycerol tri-carboxylic acid polyester foam which results in a high-quality product, and which can be carried out in a reproducible manner. There is particular need for a process for manufacturing a foam with a regular foam structure. The present invention provides such a process.
The process according to the invention comprises the steps of combining glycerol and a tri-carboxylic acid to provide a liquid reaction mixture and contacting the reaction mixture with a substrate under polymerization conditions, wherein the substrate has a top layer comprising one or more of metal, metal oxide, and metal halide.
It has appeared that the process of the invention allows the manufacture of polyester foams from glycerol and a tri-carboxylic acid, which foams have good properties while the process can be carried out in a reproducible manner, also for large reactor volumes.
The present invention will be described in more detail below.